The regulation of vaginal bleeding is an important effect impacting the choice of contraceptive methods. However, comparing vaginal bleeding control and disturbance between various contraceptive studies is often limited by the lack of uniformity in the analysis and reporting of the bleeding patterns. In 1986, the World Health Organization (WHO) issued recommendations for the standardized collection, analysis and reporting of bleeding associated with contraceptives based on 90-day reference periods. We systematically reviewed MEDLINE and EMBASE for all articles reporting bleeding data by reference periods in healthy women using oral contraception. Overall, 17 publications between 1986 and September 2006 were included for review. There was marked variability in the reporting of bleeding data with most studies reporting a few selected bleeding parameters. However, these studies showed, in general, that oral contraceptive users have the greatest bleeding (i.e., results in the highest number of bleeding/spotting days) during the first reference period which decreases by Reference Period 4. Reporting of the bleeding/spotting data using the WHO recommendations may be useful in objectively comparing vaginal bleeding patterns among different oral contraceptive products.